Conventional methods for manufacturing surface mount components, or for manufacturing circuit supporting substrates for surface mount components, typically include methods for placing conductive preforms, e.g., solder balls, solder spheres, preformed solder bumps, and the like on electronic pads arranged in a predetermined placement pattern that is sometimes called a ball grid array (BGA). The term “Solder spheres” is used herein being representative of the various form factors of conductive preforms.
A known method for placing solder bumps on electronic pads on a substrate utilizes a stencil placed over the electronic pads on the substrate to guide solder paste to flow through openings in the stencil plate onto the electronic pads. The solder paste is typically spread over the stencil using a squeegee to evenly distribute the solder paste as well as remove the excess solder paste. After the stencil is removed from the substrate, solder bumps are formed on, and remain attached to, the electronic pads. This method technically forms the solder bumps on the electronic pads and does not place solder that has been preformed on the electronic pads.
The solder paste, as formed in this method, has a tendency to develop internal structural defects, such as voids, or variation of fused solder volumes during the fusing process, thereby introducing potential defects to the manufacturing process and/or risk of failure during the life of the product. This is an undesirable consequence of this method.
A first known method for placing solder balls on electronic pads on a substrate utilizes a stencil plate placed over the electronic pads on the substrate to guide solder balls to drop through openings in the stencil plate onto the electronic pads. The electronic pads having been pre-printed with solder paste, the solder balls then adhere to the electronic pads via the solder paste. During a reflow operation, the solder balls fuse to the electronic pads on the substrate.
Besides requiring a guiding force to reliably introduce the solder balls into the openings in the stencil plate, this method additionally suffers from a hot-air knife reflow heating step that unevenly distributes heat over the solder balls in the stencil plate. Further, the heating step applied while the solder balls are in the stencil may cause the solder to melt and adhere to the stencil. Furthermore, a heating-knife motion control mechanism can be expensive.
A second known method for placing solder balls on electronic pads on a substrate utilizes tubes to hold the solder balls over the electronic pads. Each tube applies a vacuum force to hold a solder ball to the end of the tube. After locating the tubes holding the solder balls over the electronic pads, the solder balls are placed on the electronic pads by removing the vacuum force from the tubes and vertically vibrating the tubes to release the solder balls onto the electronic pads.
The apparatus for this second method tends to be complicated and can be expensive to produce and maintain. Since the solder balls are placed sequentially, the process is not conducive to cycle time. It also may not be suitable for micro-BGA placement where the pitch of the pads is very fine and requires tight tolerances in locating the solder spheres.
A third known method for placing solder balls on electronic pads on a substrate utilizes a plate with solder bumps attached to the plate in a pattern corresponding to the pattern of the electronic pads on the substrate. The solder bumps are attached to the plate by etching a pattern of openings in a photoresist mask over the plate according to a predefined artwork, and then depositing solder composition on the plate at the openings (where the plate surface is exposed) by an electroplating operation. Lastly, after removing the photoresist layer, the solder bumps remain attached to plate. The solder bumps are then placed on the electronic pads on the substrate by positioning the plate over the electronic pads to allow the solder bumps to contact the electronic pads. By heating the entire assembly, the solder bumps melt and transfer onto the electronic pads.
Hertz (U.S. Pat. No. 6,202,918) teaches a solder sphere placement apparatus which utilizes an etched stencil to create a pattern for the solder spheres and a moving backing plate for releasing the solder spheres from the etched stencil. Hertz '918 is limited in the complexity of the placement head.
Hertz (U.S. Pat. Nos. 6,230,963 and 6,510,977) teaches a laminated foil design for the solder sphere placement apparatus, reducing the complexity of the solder sphere placement apparatus of Hertz '918. Hertz '963 is limited in the requirement for a custom backing plate for each solder sphere pattern. Additionally, the design taught by Hertz is limited in that the backing plate does not support the solder sphere at the apex of the solder sphere when placed into the pattern aperture.
Hertz (U.S. Pat. No. 6,412,685) teaches a plurality of release mechanisms. Included is a vibrational release mechanism, which provides a tapping release force.
Brown, et al (U.S. Pat. No. 5,205,896) teaches applying a tapping mechanism for aiding in the transfer of the solder spheres.
Besides constituting a relatively expensive process to implement in a mass production environment or use for occasional rework, this method requires trained operators to perform numerous steps, including chemical processing steps that can subject an operator to environmental hazards. The overall process, therefore, can be environmentally unfriendly, time consuming, expensive, and generally requiring trained operators to be effective.
The use of Ball Grid Array technology is increasing as the advantages of the interconnect process are recognized. The disadvantage of this technology is where rework or salvage of components using Ball Grid Array technology is required; once the component is removed a portion of the solder spheres remains on the component and a portion of the solder spheres remains on the Printed Circuit Board (PCB). Thus, what is necessary is a low cost and efficient method and apparatus for placing conductive spheres on pads on a component, or on a substrate.
While each of these improvements has contributed to the art, the art can be improved by the utilization of a new backing member design.